This invention relates to an apparatus for treating vascular conditions with high power light beams such as lasers and a method of making such an apparatus.
The use of laser beams for treatment of medical conditions has been well known. Various devices have also been developed for application of laser energy to tissue inside of a patient.
In order to provide laser energy to tissue within a patient for such purposes as ablation of plaque from the walls of a blood vessel, a technique is required which can accurately apply the laser energy to the tissue. If the laser energy is supplied to within the patient by an optical fiber and the optical fiber leads to an optical system which directs the laser beam in the appropriate direction and through a glass hood, several problems are encountered. In particular, the laser passing through the glass window may cause the build up of burnt tissue or burnt red blood cells at and around the point at which the laser exits the glass window. This black, carbonized material would in turn absorb the laser radiation before it could strike the tissue and would block or partially block proper operation of the device. The heat would be absorbed by the glass window enclosing the fiber and would be dissipated in the surrounding tissues and fluids. Depending upon the power which is used, the glass may heat faster than the surrounding fluids can dissipate the heat and this could result in permanent damage to the glass window and the hood of which it is a part. A layer of carbon may be fused to the glass rendering the device inoperable. Alternatively, the hood itself may shatter or break loose from a catheter to which it is attached. Although the catheter may be useful at providing an optically clear flushing solution (usually saline), the solution is often not supplied to the location where it is most needed. Moreover, even if one were to displace the blood between the glass hood and the tissue with an optically clear solution such that the laser beam may properly irradiate the tissue and prevent the build up of burnt red blood cells on the hood, burnt tissue may still accumulate on the hood if it contacts the tissue. Further, such a technique would not be useful if the regions surrounding the tissue which is being subjected to laser energy cannot be cleared of blood, as is the case when one wants to perform ablation on the His bundle in the ventricular septum of the heart.
Although high temperature resistant glasses may be employed to increase the survivability of a glass hood, this still does not avoid the problem of blockage of the laser radiation and build up of heat o the hood.
A further danger of using a glass window or glass hood is that the glass might break, even if the blockage and heat build up problems are avoided. Breakage of such a glass hood would allow shards of glass into a patient This is especially dangerous in that glass is not x-ray opaque so that the pieces of glass would not be visible by fluoroscopic examination.
A further complicating factor in providing safe and effective ablation is that one must provide an optical system which is relatively simple and which has the ability to carry relatively high power densities.